Modular constant current regulator

ABSTRACT

Constant current regulator ( 10 ) for supplying electrical power corresponding to a predetermined output power, comprising a plurality of modules ( 13 ) electrically connectable for simultaneous operation to jointly provide the output power, the modules are configured for providing a module output power contributing to the output power of the regulator. Each module comprises a transformer ( 135 ) for providing galvanic insulation as required by local standards, and a microcontroller ( 231 ) for controlling operation of the module. The constant current regulator comprises a data communication network ( 17 ) configured to be connected to the microcontrollers ( 231 ) of the modules ( 13 ), wherein the microcontrollers ( 231 ) are operable to exchange data over the data communication network ( 17 ) so as to make the constant current regulator ( 10 ) modular, meaning that one or more of such modules ( 13 ) can be added to or removed from the constant current regulator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/394,910 filed on Oct. 16, 2014 that is a National Phase entry ofPCT/EP2013/063421 filed on Jun. 26, 2013 that claims priority to EPApplication No. 12173866.0, filed on Jun. 27, 2012.

TECHNICAL FIELD

The present invention relates to constant current regulators (CCRs), inparticular regulators used for supplying airfield lights with electricalpower.

BACKGROUND

CCRs of the above kind are known from e.g. US 2010/283400. A CCR's goalis to regulate a current output level around a working point which cane.g. be set by an operator or an airport control tower. The currentoutput level should be as constant as possible near to a pre-set workingpoint in order to ensure that the airfield lights emit at constantluminous intensity. Since it is desirable to use different intensitiesdepending on the circumstances (e.g. day or night, good or lowvisibility), the working point can change and the CCR must be able toadapt the current output level accordingly.

Airfield lights are typically arranged in long series connections. Thelength and number of lights in such series and hence the power to bedelivered to it can differ between airports, between the type of lightsand their use. CCR manufacturers therefore need to provide a wide rangeof CCRs, each corresponding to a particular input line voltage andfrequency, output current and equipment power. This leads to a largenumber of different CCR product items, which increases stocks,manufacturing resources and cost.

CCR reliability is another aspect, since it is an important safetyissue. It is known to have complete backup CCR units installed atairports, which requires a huge additional space and leads to asignificant cost increase.

An attempt to tackle the reliability issue is described in US2010/026207 by providing a twin voltage conversion unit connected incascade to a common transformer operating at grid frequency (50/60 Hz).The idea here is to add a redundant (non-operating) voltage conversionunit, which is easily replaceable. In the event of a failure, theoperating and non-operating voltage conversion units can be switchedautomatically, such that the broken part can be replaced later during amaintenance service.

The same document describes that it is not excluded to use the twovoltage conversion units contemporarily for the operation of the CCR,but fails to teach how the co-operation is to be carried out.Additionally, the document describes a common control unit forcontrolling operation of the voltage conversion units and for activatingswitches configured to activate and deactivate one or the other voltageconversion unit.

The system of US 2010/026207 is more reliable, but at an increasedexpense per CCR unit, since each CCR unit will now have an additionalvoltage conversion unit identical to the one already present.

Hu Wei et al., in “Input-series output-parallel AC/AC converter”, 20105th IEEE Conference on industrial electronics and applications, 1 Jun.2010, pages 1018-1022 describes a two-level AC/AC converter with a highfrequency link, which can be used in applications with high inputvoltage and relatively low output voltage. Such a circuit is notapplicable to airfield lighting installations due to its limited power.Furthermore, a disadvantage is that it is not reliable, since operationof both levels is required for obtaining a desired output.

EP 1063758 describes a power supply device comprising a plurality ofresonance type switching converters arranged in parallel. Such devicesallow for supplying a large power to a load. However, the describeddevices feature a DC output voltage, which is not workable for anairfield lighting installation, since airfield lighting installationsmust always be provided with AC current for corrosion protection of thecables and connectors, and in order to be able to use transformers toconnect the lights to the supply line for lightning protection,independently of the type of lights (incandescent or LEDs).

US 2002/0074862 describes a parallel power source system comprising aplurality of power supply units, so designed that even when one powersupply unit fails, the other power supply unit can ensure power supply.The described system, however, generates DC outputs from AC input supplyvoltages and cannot therefore be used for supplying airfield lightinginstallations. Each power supply unit comprises a high frequencytransformer supplied with a high frequency pulse current to its primarycoil.

OVERVIEW

It is an aim of the present invention to provide a constant currentregulator which overcomes the above drawbacks. In particular, it is anaim to provide a CCR which does not only address the reliability issue,but also the economical issue. It is an aim to provide a CCR which hasat least a same, and possibly better reliability. It is also an aim ofthe invention to provide a CCR which is more economical to manufacture.Yet another aim of the present invention is to provide a CCR which hasan increased lifetime and operates more efficiently.

In the view of the present inventors, system reliability can beincreased beyond the above proposed solutions, while obtaining aneconomy in manufacturing costs by building the CCR modularly with aplurality of identical modules, each module being in fact a CCR of itsown.

According to the invention there is therefore provided a constantcurrent regulator as set out in the appended claims. The CCR comprises aplurality of advantageously identically rated modules, each module beingconfigured to provide a module output current and voltage whichcontributes to the CCR's output power. According to the invention, eachmodule is in fact a CCR of its own, having its proper transformer andmicrocontroller. The CCR is provided with a data communication networkoperable to exchange data between the microcontrollers. The datacommunication is so organised that one or more modules canadvantageously be added to or removed from the CCR without affecting theability of the other modules to communicate with each other and operatesimultaneously to jointly provide the output power. As a result, a CCRis obtained which is modular to full extent, both at the input stage,and the output stage, as well as at the control level.

Whereas in US 2010/026207, modularity is restricted to the voltageconversion unit (i.e. the input stage only), in the present inventionmodularity applies to all the components of the CCR. An advantage ofsuch modularity is that CCRs with different rated outputs can beassembled based on one and a same CCR module. This drastically decreasesthe number of different parts that manufacturers need to keep in stockor produce. By way of example, CCRs of all the existing power ratingscan be made by using one and a same (small) transformer, therebyobviating the need of having different transformer sizes, from smallerones to large ones. Since larger quantities of the same transformer canbe produced, an economy of scale can be obtained. As an additionaladvantage, the full modularity enables to achieve increased reliability.Indeed, the CCRs described in US 2010/026207 will fail if the centralcontroller fails, or in case the common output stage fails. This is notthe case in CCRs of the present invention, since these stages areincluded in the modular design. The other documents discussed above donot describe such a modularity either.

Advantageous aspects are set out in the dependent claims.

According to another aspect of the invention, there is provided a modulefor use in a CCR according to the invention, as set out in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the invention will now be described in more detail withreference to the appended drawings, wherein:

FIG. 1 represents an overall diagram of a CCR according to theinvention;

FIG. 2 represents a diagram of a power module of a CCR according to theinvention;

FIG. 3 represents input and output connection schemes of the powermodules, for the exemplary case of a CCR comprising two power modules.

FIG. 3A represents a connection scheme wherein the power modules'outputs are connected in series. FIG. 3B represents a connection schemewherein the power modules' outputs are connected in parallel.

DESCRIPTION

It will be convenient to note that current and voltage levels indicatedin the present description refer to root mean square (rms) valuesthereof. Therefore 1 A refers to a 1 A rms current and 1 V refers to a 1V rms voltage.

It will be likewise convenient to note that the term ‘rated power’,‘rated current’, or ‘rated voltage’ refers to the maximum operatingpower, current or voltage respectively.

FIG. 1 depicts a schematic diagram of a CCR 10 according to theinvention, with power line input 11 for connection to an electricalpower network and power output 12 for connection to a series connection9 of lights. Series connection 9 is typically built up of series circuittransformers 92, the primary coils of which connected in the series 9and the secondary coils of which connected to the lights 91.

CCR 10 is formed out of modular units 13-1, 13-2 through 13-n, whichwill be referred to hereinafter as power modules 13. Power modules 13are connected to the power line input 11 through input power connections14, forming a wired interface between the power line input 11 and theline input 131 of each power module 13 (see FIG. 2). The power modulesare connected to the power output 12 of CCR 10 through output powerconnections 15.

Input power connections 14 provide for a parallel electrical connectionof the modules 13-1 through 13-n to the power line input 11, as isschematically represented in FIG. 3.

Referring to FIG. 2, it will be convenient to note that each powermodule 13 is in fact a constant current regulator of its own. Powermodule 13 hence is operable to provide an output power (current andvoltage), which can advantageously be directly supplied to the poweroutput 12 of the CCR 10 and hence to the series circuit 9, without anyadditional galvanic insulation or level correction.

All power modules 13-1 to 13-n are advantageously substantiallyidentical, in that they have identical maximum operating (rated) power,current and voltage. As with every CCR, each power module is alsoconfigured to output a power and to generate a current corresponding topre-set levels. The output voltage is related to the current and to theoutput resistance and can change between zero and a maximum (rated)voltage.

To do so, a power module 13 advantageously comprises input stagecircuits 132-134 and output stage circuits 136-138 galvanicallyseparated, as prescribed by local standards, such as FAA (FederalAviation Administration) or IEC (International ElectrotechnicalCommission) standards, by transformer 135. Transformer 135 may forexample provide galvanic insulation higher than or equal to 23 kV.

Input stage circuits may comprise a low pass filter 132 for filteringthe line input 131 of power module 13.

Input stage circuits comprise a voltage conversion circuit,schematically represented by blocks 133-134 in FIG. 2. Voltageconversion circuit 133-134 is advantageously configured for generating aregulated voltage widely independent of the input voltage level and ofthe frequency of the input voltage (e.g. mains frequency 50 or 60 Hz).Voltage conversion circuit advantageously comprises a rectifier block133 followed by a power inverter block 134. Rectifier block 133 can bebased on a diode bridge circuit, which is operable to transform an AC(alternating current) signal (such as an advantageously filtered lineinput, at grid frequency) to a DC (direct current) signal. Powerinverter block 134 is operable to transform the DC signal from therectifier 133 to an AC signal. It therefore advantageously comprises aLLC resonant converter circuit, possibly preceded by a power factorcorrector (PFC) circuit, advantageously an interleaving PFC.

The regulated voltage output by voltage conversion circuit 133-134 isadvantageously a high frequency AC voltage, such as of at least 1 kHz,advantageously at least 10 kHz, advantageously at least 20 kHz,advantageously at least 25 kHz, advantageously at least 30 kHz. The highfrequency AC voltage can be lower than or equal to 100 kHz. Theobtention of such high frequency signals can be accomplished by a highfrequency LLC quasi resonant converter power circuit. One such LLC quasiresonant converter power circuit is described in an internet papertitled “Phase Shifted Full Bridge LLC Resonant Converter” by MartinZhang and Sober Hu, and downloadable at the following web page, thecontents of which being incorporated herein by reference:http://blog.dianyuan.com/blog/u/42/1150776421.pdf.

An advantage of a high frequency voltage output in the input stage isthat size and weight, and hence cost of transformer 135 can besignificantly reduced. By way of example, a high frequency transformerworking at about 40 kHz is 10 to 20 times smaller in weight and sizecompared to its 50 Hz counterpart.

Additionally, at the indicated high frequency voltages, the power lossesdue to the high frequencies remain acceptable, such that an optimalbalance between size reduction and power loss is achieved.

The LLC resonant converter circuit is hence connected to the primaryside 235 of transformer 135. The secondary side 335 of transformer 135is connected to the output stage circuits 136-138, which can comprise: arectifier diode bridge circuit 136 and a transistor H-bridge invertercircuit 137, to provide a regulated module output 139 (current andvoltage). H-bridge inverter circuit 137 is advantageously configured forworking at a high frequency, such as the ones indicated hereinabove inrelation to the voltage conversion circuit 133-134. A low pass filter138 can be provided between the bridge circuit 137 and module output139. The regulated output 139 is typically, though not necessarily, alow frequency pure sine wave AC output, at grid frequency of typically50 or 60 Hz. Regulated outputs of other shapes are possible as well,such as pulsed DC.

The output low pass filter 138 is advantageously operable to filter outany signal components of the above indicated high frequency (i.e.frequency of operation of the rectifier and transistor H-bridge).Operating at such high frequencies is advantageous, since it allows formaking the output low pass filter 138 very small and economical comparedto output filters used in prior art CCRs, which typically operate atfrequencies of a few hundred Hz.

Referring to FIG. 3A, the outputs 139 of power modules 13-1 to 13-n canbe connected in series to realize a regulated output current of CCR 10being maximally the rated output current of one power module, butachieving a higher CCR output power compared to each single powermodules, since the regulated CCR output voltage is the sum of the moduleoutput voltages. By way of example, considering power modules with 5 kWrated power (on resistive load) with a rated output current of 6.6 A.The rated output voltage of each power module will then be 757 V.Connecting the power modules' outputs in series allows for obtaining aCCR output current of maximum the rated output current of a power module(6.6 A), but at variable power depending on the number of power modulesconnected in series. Connecting four such power modules in series allowsfor obtaining a CCR having a rated output power of 20 kW 6.6 A×(4×757V).

Alternatively, as represented in FIG. 3B, the outputs 139 of powermodules can be connected in parallel to obtain a CCR output currentbeing the sum of the power module outputs. By way of example, connectingthree of the above power modules in parallel allows for obtaining amaximum rated CCR output current of about 20 A at a voltage level of 757V.

It is also possible to combine series and parallel connections of powermodules, such as a series connection of two groups of two 5 kW modulesin parallel, thereby obtaining a 20 kW CCR with a maximum output currentof 12 A.

The electric connection of the power modules 13-1 to 13-n in the abovedescribed series or parallel connections, is advantageously a hard-wiredconnection.

Hence, according to the invention, all the power module outputs areconfigured to contribute to achieving the CCR (global) output 12. Thereare different ways for obtaining a co-operation between the powermodules 13 to achieve the predetermined CCR power output 12, which isset externally, such as by an airport control tower, or an operator.

An advantageous way for obtaining such a co-operation between powermodules is based on a masterless (or multi-master) data communicationprotocol. This means that none of the power modules would act as amaster module determining the contribution level of each power module tothe CCR output, but rather each power module is situated at a same levelin the power module hierarchy and each power module self-determines itsproper module output level 139 based on the predetermined output of thewhole CCR 10 (output of all power modules 13) and on the output set bythe other power modules. This is achieved by letting the power modules13 almost constantly communicate with one another to obtain an efficientco-operation.

An alternative way for obtaining co-operation and communication betweenthe modules is based on a master-slave data communication protocol. Insuch a protocol, the master advantageously can change automatically incase a power module 13 is added to or removed from the CCR 10. By way ofexample, when a power module 13 is added to the CCR, it automaticallyreceives an address for data communication, which can be based on aserial number or unique identifier of any of the power module'scomponents. The address can therefore be hardware implemented. Theaddress is compared to the addresses of the other power modules, and theprotocol can describe that e.g. the power module having the lowest orhighest address acts as master governing the data communication, theother modules being slaves. Such a procedure ensures that in case offailure of the current master, the CCR can continue to operate byautomatically providing a new master.

A master-slave protocol, wherein the master can automatically bere-assigned can also be referred to as a masterless protocol.

To implement any of the above protocols, CCR 10 advantageously comprisesa communication network 17 linked to all the power modules 13.Communication network 17 can be implemented with any topology, andadvantageously as a communication ring. It can be implemented e.g. as aCAN-bus.

In order to allow for an exchange and proper interpretation of theinformation, each power module 13 is provided with a microprocessor(microcontroller) 231 linked to communication network 17 over a datacommunication port 233. Microcontroller 231 may be operable to controlthe input stage circuits 132-134. Possibly, power module 13 comprises asecond microprocessor (microcontroller) 232 operable to control theoutput stage circuits 136-138. The output stage microprocessor 232 maycommunicate with the input stage microprocessor 231 and with thecommunication network 17 either directly, or, as shown in FIG. 2,through the input stage microprocessor 231. It is possible to integratethe output stage microcontroller 232 in the input stage microcontroller231. Galvanic insulation between the two microprocessors 231-232 can beobtained through opto-isolators 234 and/or optical transmission of data.

In case the master-slave data communication protocol discussed above isimplemented, the address allotted to each power module can be based onan electronic signature of the microcontrollers chip, which is a uniqueidentifier.

Communication network 17 can further be linked to a remote controlinterface 18 provided in CCR 10 and configured for establishing remoteconnection with any remote control entity, such as an airport controltower. Communication network 17 can be linked to a man-machine interface19 provided in CCR 10 and allowing an operator to control CCR operation,e.g. during maintenance service.

Communication network 17 is advantageously implemented with a dedicatedshared data structure which contains information relevant to thedifferent pieces of equipment. The power modules 13 and other componentsof the CCR 10, such as the remote control interface 18, are allowed tomanage the shared data structure under some priority rules.

Hence, a modularity is obtained, wherein, advantageously, CCR 10 isallowed to operate even when one or more power modules are out ofservice. It is even possible to provide one or more redundant powermodules 13 which can promptly be put in service in the event of failureof another power module. These features can be implemented in a softwareprogram which is run on the microcontroller 231.

Advantageously, the implemented data structure allows each piece ofequipment, and in particular the power modules 13, understand how theCCR 10 is assembled, such as understanding how many power modules arepresent in the CCR and how they are connected. Advantageously, theimplemented data structure allows for adding power modules or otherpieces of equipment without requiring reprogramming the CCR 10.Advantageously, the implemented data structure allows for optimizing theglobal power efficiency of the CCR by adapting the outputs of individualpower modules. This will lead to energy savings and henceenvironment-friendly operation. Advantageously, the implemented datastructure allows for reconfiguring the system in case of a fault, suchas when a power module goes down, the remaining power modules couldprovide the missing output power.

An example co-operation between power modules 13-1 to 13-n can be asfollows. An airport control tower (not shown) sets a predeterminedbrightness level (e.g. between 1 and 5), which is converted to a currentoutput level of CCR 10, which arrives through remote control interface18 on the communication network 17. The new set-point is read by all themicrocontrollers 231 of power modules 13-1 to 13-n. Depending on thedata communication (network) protocol, the microcontrollers 231 mayeither begin communicating with one another over the communicationnetwork 17 such that each microcontroller 231 establishes an outputlevel 139 for its proper power module 13, or the microcontroller 231 ofthe master power module may determine the output levels 139 for each(slave) power module upon reading the new brightness level. Consideringby way of example a CCR having three identical power modules with ratedoutput current of 6.6 A at 757 V connected in parallel, then the maximum(rated) global output of the CCR as explained above is 20 A at 757 V.Now, let the CCR output current level be set at 15 A, then themicrocontrollers 231 and possibly 232 will communicate with one anotherto eventually set the output level of each power module to 5 A. When thecontrol tower would set the CCR output current level at 7 A, possiblythe system could decide to operate two power modules at an outputcurrent level of 3.5 A, and to keep one power module inactive, since itis more efficient to operate a power module at levels close to ratedoutput level. Such control algorithms can advantageously besoftware-implemented in the microcontrollers 231 of power modules 13according to the invention.

By so doing, advantageously, the CCR output level can attain the set(predetermined) level within a few milliseconds.

The power modules 13-1 to 13-n connected in series and/or in parallel inCCR 10 are advantageously synchronized to provide current and voltageoutputs 139 which are advantageously in-phase with the line input. Thisallows for sinking a maximal output power at same time instants when theinput power from the line input is maximal. Advantageously, each moduleprovides for a proper synchronization between the output signal (atoutput 139) and the input signal (at input 131). To do so, each modulemay comprise a phase detector, possibly coupled to the input filter 132and each microcontroller 231 may read a line phase timing from the phasedetector.

A possible way of obtaining synchronization between the output signal(at output 139) and the input signal (at input 131) is byreading/detecting the zero crossings of the input signal by themicrocontroller 231. A signal synchronous with the detected zerocrossings is constructed by the microcontroller 231 (or, as the case maybe, the output stage microcontroller 232). Such a signal isadvantageously a square wave at the input line frequency, e.g. 50 Hz or60 Hz. This signal can be used by the output stage circuits to generatean output sine wave with the same zero crossings.

CCR 10 advantageously comprises an output measuring unit 16 configuredfor measuring parameters of the power output 12 of CCR 10, such asvoltage and current levels, phase information and frequency, and otherparameters relevant to module operation such as load inductance andresistance to earth. Output measuring unit 16 is advantageously linkedto the communication network 17, allowing the measured information to befed back to the power modules 13, so that they may adapt their outputs139.

Output measuring unit 16 may be configured for measuring an outputparameter representative of phase information of the output signal.Output measuring unit 16 may comprise circuitry, such as amicroprocessor, to interpret the measured output parameter in order tocalculate the resistive part and the reactive part of the load. Thisinformation can be sent over the communication network 17 tomicrocontrollers 231 which could adapt the output parameters, such asthe shape of the output power wave, to the different kinds of field(light) circuits (resistive, inductive or capacitive).

Advantageously, output measuring unit 16 is configured to measure one ormore parameters of the CCR power output 12 at time intervals smallerthan or equal to 100 μs, such as about 50 μs. The time interval betweenmeasurements can be smaller than or equal to 5 μs, advantageouslybetween 1 μs and 3 μs.

Advantageously, the modules 13 are configured for reading phase-relateddata fed by measuring unit 16 and for using the phase-related data forphase synchronization of the output. This phase synchronization based on“external” data (with regard to each module) can be provided inaddition, or in alternative to the “internal” phase synchronizationbetween the line input and the module output as described above. In caseof addition, the phase synchronization based on the “external” data canallow for improving the accuracy of the “internal” synchronization.

It will be convenient to note that since the CCR output is a lowfrequency AC signal, typically of 50 or 60 Hz, synchronization time isnot critical.

Advantageously, the power modules 231 are provided with a softwareprogram, which when run on the microcontrollers 231, is configured tooperate at least the input stages of the power modules, andadvantageously both the input and the output stages. By so doing, anenhanced system control is obtained compared to the prior art, whichincreases flexibility and reliability. This flexibility, which is inpart based on a software implementation of some functions, allows theCCR to operate in different modes according to customer requirements. A“green mode” can be implemented by switching a module completely off incase of low power output of the CCR is desired. In case speed isrequired, all the modules can be kept always on to ensure fast reactiontimes. Other modes can be implemented by updating the software programwithout any change in the hardware.

Advantageously, the microcontroller can be programmed to implement oneor more digital P/PI/PID feedback loops. Such digital control loops havethe advantage that the signals can be digitally filtered before beingapplied in the control (feedback) loop, which enables to work reliablyeven in a highly noisy environment. To this end, the power module 13advantageously comprises one or more analog to digital converters (ADC)to provide for (one-way) communication from the different blocks in boththe input stage (blocks 132-134) and the output stage (blocks 136-138)to the microcontroller(s) 231 (and 232). The ADCs and any possible DACsare represented by blocks 236 in FIG. 2.

It will be convenient to note that communication from themicrocontroller to the input/output stage blocks is typically digital.Since the electronic circuits in blocks 133, 134, 136, and/or 137 can becontrolled by pulse with modulation (PWM), signals going out from themicrocontroller in principle do not require any analog conversion.Alternatively, digital to analog converters (DAC) may be provided fortwo-way communication with the microcontroller 231 (and 232) ascircumstances may require.

One such PID feedback loop can be implemented between the power inverterblock 134 and the rectifier block 133. Microcontroller 231 may beprogrammed to read and analyse actual signals from either blocks 133 and134 digitally in order to provide for necessary control. By way ofexample, in case the power inverter block 134 is a LLC resonantconverter circuit, a signal connection with the microcontroller can beconfigured to feed the actual bus voltage of the resonant bridge to themicrocontroller. The microcontroller can be programmed to compare itdigitally with the target bus voltage. Based on the difference, themicrocontroller can be programmed to determine and/or adapt a pulsewidth modulation (PWM) scheme (duty cycle, frequency) for being appliedto the rectifier 133 in order to compensate for the difference. By sodoing, a satisfactory power factor can be obtained in every condition.Additionally, the microcontroller can be programmed to control a busvoltage of any of the output stage circuits (blocks 136, 137 or 138) byadapting the PWM scheme applied to rectifier 133.

Advantageously, the microcontroller 231 can be programmed to apply a PWMsignal to each of the two branches of the LLC resonant converter bridgein block 134, which signal can be different between the two branches.This can be obtained by implementing a second PID feedback loop in themicrocontroller 231, in addition to the one discussed above. The firstPID feedback loop is used for low load and controls the phase shiftbetween the two PWM signals provided to the two branches of the LLCresonant bridge 134. For higher loads, if the target voltage has notbeen reached at 180° phase shift (i.e. maximum output of the first PIDfeedback loop), the second PID feedback loop comes into action in orderto further increase the output voltage. It reduces the PWM signalfrequency of both branches until the desired bus voltage is attained (isread by the microcontroller 231), maintaining a 180° phase shift.

Additional digital PID feedback loops can also be implemented in thesoftware program configured to run on microcontroller 231/232 in orderto control the bus voltage of any one of the output stage circuits136-138. To this end, use can be made of pulse width modulation in theoutput stage bridges 136 and/or 137 as is known in the art. The signalconnections between bridges 136/137 and the microcontroller 231/232 canbe provided through ADCs similar to the input stage.

Advantageously, a set of different PWM signal schemes can be stored inthe microcontroller and applied by it in function of the outputwaveform, from a DC output to a high frequency AC output.

Power modules 13 according to the invention are advantageously builtsuch that they can be mounted into standard racks. CCRs of differentrated outputs according to the invention can be assembled utilising asame rack size, simply by adding one or more power modules to the rack.Whereas previously a manufacturer would have needed differenttransformers and different voltage conversion boards for CCRs ofdifferent output ratings, according to the present invention all kindsof CCRs can be assembled based on one and the same power module, whichdrastically cuts stocks and economizes manufacturing. Furthermore,operating the transformers within a power module at high frequencyfurther allows for reducing size and weight of the power modules, suchthat CCRs according to the invention have at least similar andadvantageously decreased dimensions and weight than prior art CCRs.

Power modules 13 advantageously have a power output rating smaller thanor equal to 10 kVA, advantageously smaller than or equal to 8 kVA,advantageously smaller than or equal to 6 kVA. The power output ratingof power modules 13 is advantageously at least 1 kVA, advantageously atleast 2 kVA. Indicated rating values are on resistive load. Constantcurrent regulators according to the invention advantageously comprisebetween one and ten power modules, advantageously between one and six.

The invention claimed is:
 1. A method of supplying a series circuit ofan airfield lighting installation with an electric power, comprising:operating a plurality of modules of a constant current regulator, themodules each providing a module power output, each module galvanicallyinsulating the module output from a power line input, wherein theplurality of modules are electrically connected, wherein the modulepower outputs of the plurality of modules combine to form a power outputof the constant current regulator, wherein the power output of theconstant current regulator is supplied to the series circuit; exchangingfirst data between the plurality of modules over a data communicationnetwork; and processing the first data by microcontrollers in each ofthe plurality of modules to adapt the respective module power output. 2.The method of claim 1, comprising changing a set point level for thepower output of the constant current regulator, wherein the first datais exchanged following changing the set point level.
 3. The method ofclaim 1, wherein following failure of one of the plurality of modules,exchanging second data between the plurality of modules over the datacommunication network, and the second data is processed by themicrocontrollers to determine adjusted module power output levels forthe plurality of modules.
 4. The method of claim 3, wherein each of themicrocontrollers applies a respective one of the adjusted module poweroutput levels to adapt the respective module output.
 5. The method ofclaim 1, wherein adapting the respective module power output comprisesthe respective microcontroller adapting a pulse width modulated signal.6. The method of claim 1, comprising: operating the data communicationnetwork by a master-slave protocol, which assigns one of the pluralityof modules as a master of the master-slave protocol; wherein, followingfailure of the master module, third data is exchanged between theplurality of modules over the data communication network whichre-assigns the master to a second one of the plurality of modules. 7.The method of claim 6, wherein each of the plurality of modulescomprises a unique identifier, wherein re-assigning the master comprisescomparing the unique identifiers of the plurality of modules.
 8. Themethod of claim 6, wherein the master module determines a contributionlevel for each of the plurality of modules to the electric powersupplied to the series circuit.
 9. The method of claim 1, comprising:operating the data communication network by a masterless datacommunication protocol, wherein, following one of a group consisting of:a failure of one of the plurality of modules and a change in a set-pointlevel for the power output of the constant current regulator, each ofthe microcontrollers determines an adjusted module power output level ofa respective one of the plurality of modules.
 10. The method of claim 9,wherein each of the microcontrollers applies the respective adjustedmodule power output level to adapt the respective module power output.11. The method of claim 1, comprising synchronising a phase of themodule power output of each one of the plurality of modules with thepower line input.
 12. A power module, comprising: an input circuit forreceiving a power line input signal; an output circuit for providing anoutput power signal; a transformer providing galvanic insulation betweenthe input circuit and the output circuit; a first controller operable tocontrol operation of one of a group consisting of the input circuit, theoutput circuit, and both the input circuit and output circuit; and adata communication port coupled with the first microcontroller; thefirst microcontroller is operable to communicate via the datacommunication port with at least one other power module to determine anappropriate power level of the output power signal to combine with apower signal of the at least one other power module, to supply apredetermined output power; and wherein the first microcontroller isoperable control the operation of the one of a group consisting of theinput circuit, the output circuit, and both the input circuit and outputcircuit to achieve the appropriate power level.
 13. The power module ofclaim 12, wherein the first controller controls the operation of theinput circuit; the power module further comprises a second controlleroperable to control the operation of the output circuit; and wherein thesecond controller is operable to communicate with the first controller.14. The power module of claim 13, further comprising an opto isolatorcircuit coupled with the first controller and the second controller;wherein the first controller communicates with the second controller viathe opto isolator circuit.
 15. The power module of claim 13, wherein thefirst controller is operable to synchronize the output power signal withthe power line input signal.
 16. The power module of claim 15, whereinthe first controller synchronizes the output power signal with zerocrossings of the input signal.
 17. The power module of claim 16, whereinthe second controller is operable to generate the output power signalwith zero crossings corresponding with the zero crossings of the inputsignal.
 18. The power module of claim 16, further comprising a phasedetector coupled with the first controller.
 19. The power module ofclaim 12, wherein the first controller is operable to employ acommunication protocol for communicating with the least one other powermodule that allows for automatic reconfiguration of the power moduleupon one of a group consisting of detecting a new power module incommunication with the data communication port and losing communicationwith a power module coupled with the data communication port.
 20. Aconstant current regulator for supplying a predetermined output power,the constant current regulator comprising: a plurality of power moduleselectrically coupled with each other to jointly provide thepredetermined output power, individual modules belonging to theplurality of power modules comprise a transformer for providing galvanicinsulation, and a microcontroller for controlling the operation of themodule; wherein the individual modules belonging to the plurality ofpower modules provide a module output power that contributes to thepredetermined output power; and a data communication networkcommunicatively coupling the plurality of modules; wherein themicrocontrollers of the individual modules belonging to the plurality ofmodules communicate with each other via the data communication networkto cooperate and achieve the predetermined output power.